1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device in which a support substrate has a metallic part produced by plating and its remaining part made of semiconductor.
2. Description of the Background Art
In packaging a semiconductor device, a support substrate, prepared by one of the following two methods, is used to facilitate handling of the device.
The first method will now be described with reference to FIGS. 6A to 6D, according to an article, “Now, come out to the field! GaN Electronic Device” Semiconductor Industry Newspaper Forum, 2003, for example. Initially, a metal wiring 150, which functions as an electrode or connection, is formed on an underlying substrate 130. The surface of the underlying substrate 130 and the metal wiring 150 are buried by a surface protective film 160 to prepare a semiconductor wafer, as shown in FIG. 6A. The underlying substrate 130 is then worked into a thin film, 30 to 50 μm thick, to yield a support substrate 132 as the underlying substrate reduced in thickness, as shown in FIG. 6B. A metallic film 120 is then formed by sputtering or plating on the reverse side of the support substrate 132, FIG. 6C. Finally, the semiconductor wafer is separated into chips by, e.g. dicing, as shown in FIG. 6D.
The second method will now be described with reference to FIGS. 7A to 7D, according to U.S. Pat. No. 5,504,036 to Dekker et al., and P. G. M. Baltus, et al., “A 3.5-mW, 2.5-GHz Diversity Receiver and a 1.2-mW, 3.6-GHz VCO in Silicon on Anything”, IEEE Journal of Solid-State Circuits, Vol. 33, No. 12 pp. 2074-2079 (1998), for example. In the second method, a metal wiring 150, which functions as an electrode or a connection, is formed on an SOI substrate 135, composed of an underlying semiconductor layer 136, a buried oxide (BOX) layer 137 on the underlying semiconductor layer 136, and an SOI layer 138 on the BOX layer 137. The surface of the SOI substrate 135 and the metal wiring 150 are buried by a surface protective film 160 to prepare a semiconductor wafer, as shown in FIG. 4I. Another support substrate 180 of an insulating or electrically conductive material is then stuck on the surface protective film 160, using an adhesive 170, such as an epoxy adhesive or an acrylate adhesive, as shown in FIG. 7B. The underlying semiconductor layer 136 of the SOI substrate 135 is then etched or ground off, as shown in FIG. 7C. Finally, the semiconductor wafer is separated into chips by, e.g. dicing, as shown in FIG. 7D.
With the above-described first method, the silicon substrate, functioning as a support substrate, is poor in heat dissipation performance. So, the semiconductor device, which includes the substrate and evolves much heat, is likely to be deteriorated in performance. The second method, in which the additional support substrate is stuck onto the semiconductor wafer by means of adhesive, is difficult to apply to a device, which evolves much heat, from the standpoint of thermal resistance of the adhesive.
The third method has been reported, in which, after the underlying semiconductor substrate on the reverse side is completely removed, a plating layer is formed on the reverse surface, and used as a new support substrate, see Japanese Patent Laid-Open Publication No. 2003-197980, for example.
The fourth method has been proposed, in which a portion of a support substrate, from which heat is to be dissipated, is formed by a thin film and a plating layer is formed on this thin film, see Japanese Patent Laid-Open Publication No. 2004-71886, for example.
With the above-described third method, there is fear that the substrate becomes warped due to the stress in the plating layer served as a support substrate, and hence the product is difficult to use in the from of semiconductor device.
With the fourth method, the semiconductor support substrate persists in an active region in need of heat dissipation, and hence the heat dissipation is not sufficient. In this case, the semiconductor device is likely to be deteriorated in performance.
With this in mind, the inventor of the present patent application has conducted eager searches, and has found that the support substrate has its metal part formed by plating and extending across the entire thickness of the support substrate, and its remaining portion made of semiconductor to form a semiconductor device, which is superior in heat dissipation performance, there being no warping of the substrate otherwise caused by the stress in the plated layer.
The present inventor has particularly found that the support substrate has its metal part formed immediately below the active region of a semiconductor device, through which flows the current in operation of the semiconductor device, and its other portion immediately below the inactive region of the semiconductor device made of semiconductor, so that heat dissipation may be carried out more effectively.